Control of processing elements in parallel processors

ABSTRACT

The present invention relates to the control of an array of processing elements in a parallel processor using row and column select lines. For each column in the array, a column select line connects to all of the processing elements in the column. For each row in the array, a row select line connecting to all of the processing elements in the row. A processing element in the array may be selected by activation of its row and column select lines.

FIELD OF THE INVENTION

[0001] The present invention relates to the control of processing elements in a parallel processor. Preferred embodiments of the present invention relate to the control of an array of processing elements in an active memory device.

BACKGROUND TO THE INVENTION

[0002] A simple computer generally includes a central processing unit (CPU) and a main memory. The CPU implements a sequence of operations encoded in a stored program. The program and the data on which the CPU acts are typically stored in the main memory. The processing of the program and the allocation of main memory and other resources are controlled by an operating system. In operating systems where multiple applications may share and partition resources, the processing performance of the computer can be improved through use of active memory.

[0003] Active memory is memory that processes data as well as storing it. It can be instructed to operate on its contents without transferring its contents to the CPU or to any other part of the system. This is typically achieved by distributing parallel processors throughout the memory. Each parallel processor is connected to the memory and operates on it independently. Most of the data processing can be performed within the active memory and the work of the CPU is thus reduced to the operating system tasks of scheduling processes and allocating system resources.

[0004] A block of active memory typically consists of the following: a block of memory, e.g. dynamic random access memory (DRAM), an interconnection block and a memory processor (processing element array). The interconnection block provides a path that allows data to flow between the block of memory and the processing element array. The processing element array typically includes multiple identical processing elements controlled by a sequencer. Processing elements are generally small in area, have a low degree of hardware complexity, and are quick to implement, which leads to increased optimisation. Processing elements are usually designed to balance performance and cost. A simple more general-purpose processing element will result in a higher level of performance than a more complex processing element because it can ,easily be coupled to many identical processing elements. Further, because of its simplicity, the processing element will clock at a faster rate.

[0005] In any computer system, it is important that data can be made available to the processor as quickly as possible. In a parallel processor, the organisation of data in the processing element array is an important part of the execution of many algorithms. Hence, the provision of an efficient means of moving data from one processing element to another is an important consideration in the design of the processing element array.

[0006] In the past, several different methods of connecting processing elements have been used in a variety of geometric arrangements, including hypercubes, butterfly networks, one-dimensional strings/rings and two-dimensional meshes In a two-dimensional mesh, the processing elements are arranged in rows and columns, with each processing element being connected to its four neighbouring processing elements in the rows above and below and the columns either side (directions herein referred to as north, south, east and west).

[0007] In current systems, movement of data between the processing elements generally occurs as a parallel operation, i.e. every processing element sends and receives data from other processing elements at the same time. Data can be viewed as being shifted in one of four directions (north, south, east and west) along all of the processing elements in the rows or columns.

[0008] In addition, there may also be a column of edge registers located along an east or west side of the processing element array and a row of edge registers located along an north or south side, each register being connected to the processing elements at both ends of every row or column. The edge registers permit data to be shifted into or out of the processing element array as data is shifted along the rows or columns.

[0009] One problem with current system and methods of shifting data between processing elements in a processing element array is that every processing element has to send and receive data at the same time. Thus, movement of data around the processing element array can generally only occur in a limited number of different transformations and movement of data between two processing elements, which are not neighbours, has to take place over a number of shift operations. It is therefore desirable to reduce the number of shift operations that are required to move data between non-neighbouring processing elements.

[0010] Accordingly, it is an object of the present invention to provide a more efficient means of moving data from one processing element to another.

[0011] It is a further object of the present invention to provide a more flexible parallel processor in which data can be moved easily between non-neighbouring processing elements in a single operation.

SUMMARY OF THE INVENTION

[0012] In view of the foregoing and in accordance with one aspect of the present invention, there is provided a parallel processor comprising:

[0013] an array of processing elements arranged in rows and columns;

[0014] for each column in the array, a column select line connecting to all of the processing elements in the column; and

[0015] for each row in the array, a row select line connecting to all of the processing elements in the row,

[0016] wherein a processing element in the array may be selected by activation of its row and column select lines.

[0017] Thus, a given processing element can easily be selected by specifying its row and column. A plurality of processing elements in a particular row can be selected by activating a row select line and further activating one or more column select lines. A plurality of processing elements in a particular column can be selected by activating a column select line and further activating one or more row select lines.

[0018] Preferably, for each row in the array, there is provided:

[0019] a column edge register; and

[0020] a row bus,

[0021] the row bus connecting to all of the processing elements in the row and the relevant column edge register.

[0022] In a first configuration of the parallel processor:

[0023] each processing element is adapted to load a value from the relevant row bus when elected by its row and column select lines; and

[0024] the relevant column edge register is adapted to drive a value onto the row bus.

[0025] Thus, in a particular row, a value stored in the relevant column edge register can easily be loaded into one or more of the processing elements in the row by simply activating the relevant row select line and the column select lines for the processing elements into which the value is to be loaded. There is no requirement to address each processing element in turn to load them with values.

[0026] The row bus may connect the relevant column edge register and all of the processing elements in the row in series. Preferably then, in a second configuration of the parallel processor:

[0027] each processing element is further adapted to output onto the row bus a new value that is the logical combination of the value it loads from the row bus and a value internal to the processing element, when selected by its row and column select lines; and

[0028] the relevant column edge register is further adapted to load from the row bus the said new value output by the last of the processing elements in the series.

[0029] Thus, in a particular row, processing elements can easily be selected to input into the relevant column edge register a logical combination of values stored in the selected processing elements. Again, there is no requirement to address each processing element in turn to output to the column edge register a logical combination of the values stored in them.

[0030] Preferably, the said logical combination is a logical product.

[0031] Preferably, for each column in the array, there is provided:

[0032] a row edge register; and

[0033] a column bus,

[0034] the column bus connecting to all of the processing elements in the row and the elevant row edge register.

[0035] In a third configuration of the parallel processor:

[0036] each processing element is adapted to load a value from the relevant column bus, when selected by its row and column select lines; and

[0037] the relevant row edge register is adapted to drive the value onto the column bus.

[0038] Thus, in a particular column, a value stored in the relevant row edge register can easily be loaded into one or more of the processing elements in the column by simply activating the relevant column select line and the row select lines for the processing elements into which the value is to be loaded.

[0039] The column bus may connect the relevant row edge register and all of the processing elements in the column in series. Preferably then, in a fourth configuration of the parallel processor:

[0040] each processing element is further adapted to output onto the column bus a new value that is the logical combination of the value it loads from the column bus and a value internal to the processing element, when selected by its row and column select lines; and

[0041] the relevant row edge register is further adapted to load from the column bus the said new value output by the last of the processing elements in the series.

[0042] Thus, in a particular column, processing elements can easily be selected to input into the relevant row edge register a logical combination of values stored in the selected processing elements.

[0043] Preferably, said logical combination is a logical product.

[0044] In a fifth configuration of the parallel processor, each processing element is connected to one or more neighbouring processing elements and is adapted to load one or more values from one or more neighbouring processing elements when selected by its row and column select lines.

[0045] Thus, values stored in the processing elements can easily be shifted along a row or column and selectively loaded into chosen processing elements.

[0046] Although first to fifth configurations of the parallel processor have been mentioned, a parallel processor according to the present invention may be capable of adopting none, one, several or all of such configurations. There is no implication that a parallel processor that is capable of adopting the third configuration must also be capable of adopting the first and second configurations, although that is preferred.

[0047] Preferably, in each processing element, there is provided:

[0048] a neighbourhood connection register; and

[0049] a selection circuit having a plurality of inputs and an output connected to an input of the neighbourhood connection register,

[0050] wherein the selection circuit is adapted to select one of the plurality of inputs and output a value from the selected input to the neighbourhood connection register.

[0051] Additionally, there may be a control circuit in each processing element which receives and decodes control signals transmitted to all of the processing elements.

[0052] Preferably, there is provided, in each processing element, an interconnect circuit having a plurality of inputs, a column output and a row output,

[0053] wherein:

[0054] a first input to the interconnect circuit is an output of the neighbourhood connection register;

[0055] a second input to the interconnect circuit is the column output of the interconnect circuit in a neighbouring processing element in the column containing the processing element;

[0056] a third input to the interconnect circuit is the row output of the interconnect circuit in a neighbouring processing element in the row containing the processing element; and

[0057] the interconnect circuit is connected to the control circuit and is configured by the control circuit to direct to the column output either a value at the first input or a logical combination of a value at the first input and the second input and to direct to the row output either a value at the first input or a logical combination of a value at the first input and the third input.

[0058] Preferably, the logical combination is a logical product of the value at the first input and the second input or a logical product of the value at the first input and the third input.

[0059] Preferably, a first input to the selection circuit is an output of the neighbourhood connection register in a neighbouring processing element on a first side in the column containing the processing element;

[0060] a second input to the selection circuit is the column output of the interconnect circuit in a neighbouring processing element on a second side opposite to the first side;

[0061] a third input to the selection circuit is an output of the neighbourhood connection register in a neighbouring processing element on a third side in the row containing the processing element;

[0062] a fourth input to the selection circuit is the row output of the interconnect circuit in a neighbouring processing element on a fourth side opposite to the third side; and

[0063] the control circuit is connected to the selection circuit and determines which one of the plurality of inputs outputs a value to the neighbourhood connection register.

[0064] Preferably, in a processing element at the edge of the array not having a neighbouring processing element on the second side, the selection input corresponding to the neighbouring processing element is instead an output of the column edge register corresponding to the row of the processing element.

[0065] Preferably, in a processing element at the edge of the array not having a neighbouring processing element on the fourth side, the fourth input to the selection circuit is an output of the row edge register corresponding to the column of the processing element.

[0066] In accordance with a second aspect of the present invention, there is provided an active memory device comprising:

[0067] a plurality of processing elements arranged in rows and columns;

[0068] for each column:

[0069] a row edge register;

[0070] a column select line connecting to all of the processing elements in the column;

[0071] a column bus connecting to all of the processing elements in the column and the relevant row edge register;

[0072] for each row:

[0073] a column edge register;

[0074] a row select line connecting to all of the processing elements in the row; and

[0075] a row bus connecting to all of the processing elements in the row and the relevant column edge register,

[0076] wherein, for each processing element which is selected by activation of its row and column select lines, the relevant column edge register is adapted to drive a value onto the row bus and/or the relevant row edge register is adapted to drive a value onto the column bus, and each selected processing element is adapted to load the value from the its row bus and/or the value from its column bus.

[0077] In accordance with a third aspect of the present invention, there is provided an active memory device comprising:

[0078] a plurality of processing elements arranged in rows and columns;

[0079] for each column:

[0080] a row edge register;

[0081] a column select line connecting to all of the processing elements in the column;

[0082] a column bus connecting to all of the processing elements in the column and the relevant row edge register in series;

[0083] for each row:

[0084] a column edge register;

[0085] a row select line connecting to all of the processing elements in the row; and

[0086] a row bus connecting to all of the processing elements in the row and the relevant column edge register in series,

[0087] wherein:

[0088] each processing element, when selected by activation of its row and column select lines, is adapted to output onto the row bus a first value that is the logical combination of a value it loads from the row bus and a value internal to the processing element and is further adapted to output onto the column bus a second value that is the logical combination of a value it loads from the column bus and the value internal to the processing element,

[0089] the relevant column edge register is further adapted to load from the row bus the said first value output by the last of the processing elements in the series in the row; and

[0090] the relevant row edge register is further adapted to load from the column bus the said second value output by the last of the processing elements in the series in the column.

[0091] In accordance with a fourth aspect of the present invention, there is provided an active memory device comprising:

[0092] a plurality of processing elements arranged in rows and columns;

[0093] for each column in the array, a column select line connecting to all of the processing elements in the column; and

[0094] for each row in the array, a row select line connecting to all of the processing elements in the row,

[0095] wherein each processing element is connected to one or more neighbouring processing elements and is adapted to load one or more values from one or more of the neighbouring processing elements when selected by activation of its row and column select lines.

[0096] In accordance with a fifth aspect of the present invention, there is provided a method of operating a processing element in an array of processing elements arranged in rows and columns in a parallel processor, wherein there is provided for each column in the array, a column select line connecting to all of the processing elements in the column, and for each-row in the array, a row select line connecting to all of the processing elements in the row, the method comprising the step of:

[0097] selecting a processing element in the array by activating its row and column select lines.

[0098] In one embodiment of the present invention, for each row in the array, there is provided a column edge register and a row bus, the row bus connecting to all of the processing elements in the row and the relevant column edge register, the method further comprising:

[0099] outputting a value stored in the column edge register corresponding to the selected processing element onto the row bus for the row; and

[0100] loading the selected processing element with the value on the row bus.

[0101] In a second embodiment of the present invention, there is further provided a row bus connected to the relevant column edge register and all of the processing elements in the row in series, the method comprising:

[0102] outputting a value from each selected processing element to the row bus;

[0103] logically combining the value with all other values output to the row bus from other selected processing elements in the row to generate a new value on the row bus; and

[0104] loading the column edge register with the new value from the row bus.

[0105] In a third embodiment of the present invention, for each column in the array, there is provided a row edge register and a column bus, each column bus connecting to all of the processing elements in the column and the relevant row edge register, the method comprising:

[0106] outputting a value stored in the row edge register corresponding to the selected processing element onto the column bus for the column; and

[0107] loading the selected processing element with the value on the column bus.

[0108] In a fourth embodiment of the present invention, there is further provided a column bus connected to the relevant row edge register and all of the processing elements in the column in series, the method comprising:

[0109] outputting a value from each selected processing element to the column bus;

[0110] logically combining the value with all other values output to the column bus from other selected processing elements in the column to generate a new value on the column bus; and

[0111] loading the row edge register with the new value from the column bus.

[0112] In a fifth embodiment of the present invention, the method comprises

[0113] outputting a value from a neighbouring processing element to the selected processing element; and

[0114] loading the value into the selected processing element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0115] A specific embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0116]FIG. 1 shows one embodiment of an active memory block in accordance with the present invention;

[0117]FIG. 2 shows one embodiment of a partitioned active memory block in accordance with the invention;

[0118]FIG. 3 shows one embodiment of the layout of components in a processing element of the present invention;

[0119]FIG. 4 shows one embodiment of a processing element array interconnect logic in accordance with the invention;

[0120]FIGS. 5a to 5 d show shift operations which can be carried out in accordance with the present invention;

[0121]FIG. 6 shows one embodiment of a broadcast operation in accordance with the present invention;

[0122]FIG. 7 shows on embodiment of a broadcatch operation in accordance with the present invention; and

[0123]FIGS. 8a and 8 b show an example array transformation operation that can be carried out in accordance with the present invention.

DETAILED DESCRIPTION

[0124] Referring to FIG. 1, one embodiment of an active memory block in accordance with the invention is shown. Active memory block 100 includes a memory 106 and memory processors 110. Memory 106 is preferably random access memory (RAM), in particular dynamic RAM (DRAM). Memory processors 110, which include processing element (PE) arrays, can communicate with memory 106 via an interconnection block 108. The interconnection block 108 can be any suitable communications path, such as a bi-directional high memory bandwidth path. A central processing unit (CPU) 102 can communicate with active memory block 100 via a communications path 104. The communications path 104 may be any suitable bi-directional path capable of transmitting data.

[0125] Referring to FIG. 2, a processing element array 200 having multiple processing elements arranged in rows and columns is shown. The array 200 is shown as an array of 4 columns×4 rows. However, it will be appreciated that the array 200 could be scaled to larger sizes and could have unequal numbers of rows and columns. However, in general, the array is likely to have 16 rows and 16 columns. For clarity, the array 200 is shown with connections along a single row 210 and a single column 212 only, although, in practice, there would be similar connections on all of the rows and columns. In particular, the present invention will be discussed below in connection with a processing element 202 a, although those of ordinary skill will recognise that every processing element in the processing element array will operate in a similar way.

[0126] The processing element 202 a is configured to accept and process a data from neighbouring processing elements 202 n, 202 e, 202 s, 202 w and is connected to the neighbouring processing elements 202 n, 202 e, 202 s, 202 w via interconnects 208 n, 208 e, 208 s, 208 w. The neighbouring processing elements 202 n, 202 e, 202 s, 202 w lie each side of the processing element 202 a in neighbouring rows and columns and can be referred to as a north neighbouring processing element 202 n, an east neighbouring processing element 202 e, a south neighbouring processing element 202 s and a west neighbouring processing element 202 w corresponding to conventional notation and as shown in FIG. 2.

[0127] Each interconnect 208 n, 208 e, 208 s, 208 w comprises an input and an output interconnect, each of which includes a network of wires to transfer data between the processing elements. The number of wires equals the number of processing element bits (e.g. 8 bits) in data input or output from the processing element 202 a.

[0128] Along one vertical edge of the array 200 are column edge registers 204, each column edge register is connected via a first bi-directional register interconnect 220 to a neighbouring processing element in its row and via a second bi-directional interconnect 222 to the processing element at the other vertical edge in its row. Along one horizontal edge of the array 200 are row edge registers 206, each row edge register is connected via a first bi-directional register interconnect 230 to a neighbouring processing element in its column and via a second bi-directional interconnect 232 to the processing element at the other vertical edge in its column. The column and row edge registers 204, 206 are connected to row and column select lines 214, 216 respectively.

[0129] Each processing element is also connected to the row select line 214 and the column select line 216. Activation of a row select line 214 and a column select line 216 connected to the processing element 202 a selects the processing element 202 a for control (e.g. to receive from or output data to a neighbouring processing element). The data may be output directly from the processing element 202 a or may be data that is merely being passed on from one neighbouring processing element to another neighbouring processing element in the same row 210 or column 212 (e.g. from the west neighbouring processing element 202 w to the east processing element 202 e.

[0130] Referring to FIG. 3, the components of the processing element 202 a are shown. The processing element 202 a includes processing logic 302, a result pipe 304 including result registers 306 and a neighbourhood connection register 308. The result pipe 304 is connected to a DRAM interface 310 via a register file 312. Data is passed between the memory 106 and the processing element 202 a via the DRAM interface 310 and the register file 312. Data is passed from the result registers 306 to the processing logic 302 to be processed. The processing logic 302 passes results of processing back to the result registers 306. Data from the north, east, south and west neighbouring processing elements 202 n, 202 e, 202 s, 202 w is received via selection logic 315 from input interconnects 350 n, 350 e, 350 s, 350 w into the neighbourhood connection register 308. Data is output to the north neighbouring processing element 202 n and the west neighbouring processing element 202 w via north/west output interconnect 352 nw from the neighbourhood connection register 308.

[0131] The north/west output interconnect 352 nw is also connected to and inputs data into interconnect logic 316 in the processing element 202 a. In addition, the north and west input interconnects 350 n, 350 w are connected to and input data into the interconnect logic 316. Data is output from the interconnect logic 316 to the south processing element 202 s and the east processing element 202 e via east and south output interconnects 352 e, 352 s.

[0132] Control logic 314 is connected to the interconnect logic 316, the processing logic 302 and the selection logic 315. The control logic 314 sends signals to the selection logic 315 to select which data should be loaded into neighbourhood connection register 308, i.e. from which of the north, south, east and west neighbouring processing elements 202 n, 202 s, 202 e, 202 w data should be loaded.

[0133] Interconnect control signals 318 received from the control logic 314 determine the output of the interconnect logic 316.

[0134] With one configuration of interconnect control signals 318, data received by the interconnect logic 316 from the neighbourhood connection register 308 is merely output to the east and south output interconnects 352 e, 352 s. Such a configuration allows data to be shifted from the processing element to the east or south neighbouring processing elements.

[0135] With another configuration of interconnect control signals 318, data from the preceding processing element in its row and/or column (i.e. the north and/or west neighbouring processing element 202 n, 202 w is merely passed on to the next processing element in series its row and/or column (i.e. the east and/or south neighbouring processing element 202 e, 202 s. Thus, the north and west input interconnects 350 n, 350 w are effectively connected to the south and east output interconnects 352 s, 352 e respectively, thereby acting as a column or a row bus for all of the processing elements in a given row or column. Such a configuration permits data from the row and/or column edge registers to be broadcast to selected processing elements in the array 200.

[0136] With yet another configuration of interconnect control signals 318, data received by the interconnect logic 316 from the neighbourhood connection register 308 via the north/west output interconnect 350 nw is logically combined with data received via the north and/or west input interconnects 350 n, 350 w from the north and/or west neighbouring processing element 202 n, 202 w. The resulting logical combination(s) is/are passed on to the next processing element in series in the row and/or column (i.e. the south and/or east processing element 202 s, 202 e. Thus, in such a configuration, the east and south output interconnects 352 e, 352 s simulate row and/or column buses connecting all the processing elements in a row or a column. The row and column buses acts as if driven by open drain drivers (i.e. the value on any bit is the wire-AND of all the processing elements' outputs in a given row or column). In fact, at a given point, data on the south and east output interconnects 352 s, 352 e between two processing elements will not necessarily be the wire-AND of all the processing elements in their row or column, but the wire-AND from all the preceding processing elements in the row or column up to that point. Thus, the east and south output interconnects 352 e, 352 s do not form “real” buses in the conventional sense, but simulate the effect of a bus to a row or column edge register connected to the last processing element in the column or row. This way, logical combinations of data can be selectively loaded (“broadcatch”) into the row and column edge registers from one or more processing elements in the array 200.

[0137] The interconnect control signals 318 are generated by the control logic 316 from the status of the row and column select lines 214, 216 and array control signals 380, which are sent globally to all of the processing elements in the array 200.

[0138] Referring to FIG. 4, one embodiment of the interconnect logic 316 in the processing element 202 a is shown. The output, X, of the neighbourhood connection register 308 (i.e. the north/west output interconnect 352 nw is connected to a first OR gate 412 and a second OR gate 422. The north input interconnect 350 n, with value X_N, is connected to a third OR gate 414 and the west input interconnect 350 w, with value X_W, is connected to a fourth OR gate 424. The interconnect control signals 318 from the control logic 314 comprise CHAIN_N 450 and XEN_N 452.

[0139] CHAIN_N 450 is input to the third and fourth OR gates 414, 424 and XEN_N 452 is input to the first and second OR gates 412 and 422. A first AND gate 416 generates a logical product of outputs from the first and third OR gates 412, 414 and a second AND gate 426 generates a logical product of outputs from the second and fourth OR gates 422, 424. The east output interconnect 352 e receives an output, X_ROW, of the second AND gate 426. The south output interconnect 352 s receives an output, X_COL, of the first AND gate 416.

[0140] The operation of the interconnect logic 316 in FIG. 4 is given in Table 2 below, where A, B and C represent sample values at inputs to the interconnect logic 316: TABLE 1 Interconnect circuit operation X_N X_W X CHAIN_N XEN_N X_ROW X_COL 350n 350s 352nw 450 452 352e 352s Function A B C 0 0 B & C A & C Broadcatch A B C 0 1 B A Broadcast A B C 1 0 C C Shift

[0141] As can be seen from Table 2, with CHAIN_N and XEN_N both being zero, the values output to the east and south output interconnects 352 e, 352 s are the values from the north and west neighbouring processing elements 202 n, 202 s ANDed with the value from the neighbourhood connection register 308 of the current processing element 202 a.

[0142] To simply pass a value from the north or west neighbouring processing element 202 n, 202 s in the row or column of the current processing element 202 a on to the south or east neighbouring processing element 202 s, 202 e, CHAIN_X is set at zero and XEN_N is set with the value 1. Thus, the row and/or column edge registers 204, 206 can broadcast their values to selected processing elements in the array 200.

[0143] To pass a value stored in the neighbourhood connection register 308 of the current processing element 202 a on to the south or east neighbouring processing element 202 s, 202 e, CHAIN_X is set with the value 1 and XEN_N is set at zero.

[0144] The control circuit 314 generates the interconnect control signals 318, CHAIN_N and XEN_N, from the set of array control signals 380 sent to all of the processing elements in the array 200. In total, there are 67 control signals, which are encoded as a 57 bit processing element instruction sent to all of the processing elements in the array 200. The control logic 3.14 uses 8 of the array control signals 380 shown in Table 2 below to control the transfer of data around the array 200. TABLE 2 Control signals controlling transfer of data in the array ARRAY CONTROL WIDTH/ SIGNAL bits SEL_X 2 LX_X 1 COND_X 1 SHIFT 1 SHIFT_LR 1 SHIFT_UD 1 BROADCAST 1 BROADCATCH 1

[0145] The array control signal, SEL_X, is generated by the control logic 314 from the value on the row and column select lines 214, 216 (i.e. one of its bits has the value of ROW_SEL and the other has the value of COL_SEL, where ROW_SEL and COL_SEL refer to the binary values on the row and column select lines 214, 216.

[0146] The array control signal, LX_X is an unqualified load enable for the neighbourhood connection register 308 in each processing element. LX_X is qualified by SEL_X to enable the neighbourhood connection register 308 to be loaded with one of the values at the north, south, east or west input interconnects 350 n, 350 s, 350 e, 350 w.

[0147] The array control signal, BROADCAST, signals to the processing elements in the array 200 that the row and column edge registers 204, 206 are broadcasting their values to all of the processing elements in their corresponding row or column. As such, the interconnect logic 316 is set-up such that north and west input interconnects 350 n, 350 w and south and east output interconnects 352 s, 352 e become row and column buses 214, 216 (as described above).

[0148] The array control signal, BROADCATCH, signals to the processing elements in the array 200 that the row and column edge registers 204, 206 are catching (i.e. being loaded with) a logical combination of the values from selected processing elements in their row or column. As such, the interconnect logic 316 is set-up such that each processing element outputs via east and south output interconnects 352 e, 352 s to the next processing element in series in its row and/or column a logical combination of the value received from preceding processing elements and the value from the current processing element 202 a.

[0149] The array control signal, SHIFT, signals to the processing elements that each processing element transfer its value in the neighbourhood connection register 308 along its row or column to the next processing element in series in its row and/or column.

[0150] The array control signals, SHIFT_UD and SHIFT_LR, qualify the SHIFT control signal and the direction in which the processing elements should transfer their values to neighbouring processing elements. SHIFT_UD signals that the current processing element 202 a should transfer its value to the south neighbouring processing element 202 s. SHIFT_LR signals that the current processing element 202 a should transfer its value to the east neighbouring processing element 202 e. The control logic 314 sends appropriate signals to the selection logic 315 to ensure that values are loaded into the current processing element 202 a according to the status of SHIFT_UD and SHIFT_LR. For example, if SHIFT_UD is activated, then the control logic 314 signals to the selection logic 315 that data is to be loaded from the north neighbouring processing element 202 n.

[0151] The array control signals, CHAIN_N and XEN_N, are generated in the control circuit as follows:

[0152] XEN_N=!(SHIFT or (BROADCATCH and ((SHIFT_UD and ROW_SEL) or (SHIFT_LR and COL_SEL)))

[0153] CHAlN_N=!(BROADCAST or BROADCATCH)

[0154] Referring to FIGS. 5a to 5 e, different operations of shifting values between the processing elements in the array 200 are shown (i.e. when the interconnection logic in each processing element is set-up, as described above, to pass a value from one processing element to a neighbouring processing element). Only operations in which values are shifted along rows of the array 200 are shown. However, it will be appreciated by those skilled in the art that values could also be shifted along columns of the processing element array in a similar manner.

[0155] In FIG. 5a, an edge shift operation is shown for a individual row 210, in which a column edge register value 500 in the column edge register 204 is loaded into a first processing element 511 as values 501, 502 in the first processing element 511 and processing elements 512 are shifted along the row 210 by being selectively loaded into their neighbouring processing elements in series in the row 210. A value 503 in a last processing element 513 at the end of the row is loaded into the column edge register 204. This way, values can be shifted in and out of the column edge registers into and out of the array 200.

[0156] In FIG. 5b, an planar shift operation for an individual row 210 is shown, in which the column edge register value 500 in the column edge register 204 is loaded into the first processing element 511 as values 501, 502 in the first processing element 511 and the processing elements 512 are shifted along the row 210 by being selectively loaded into their neighbouring processing elements in series in the row 210. The value 503 in the last processing element 513 at the end of the row 210 is not loaded into the column edge register 502, instead the value 503 is merely overwritten by a value being loaded into the last processing element 513. The column edge register value 500 is not overwritten and therefore does not change. This way, values can be shifted out of the column edge registers into the array 200 without values in the column edge registers changing.

[0157] In FIG. 5c, a wrap shift operation for an individual row 210 is shown, in which values 502 in the first processing element 511 and the processing elements 512 are shifted along the row 210 by being loaded into their neighbouring processing elements in series in the row 210. A value 503 in the last processing element 513 is loaded into the first processing element 501. This way, values can be shifted along the rows of the array 200, without affecting the contents of the column edge registers.

[0158] In FIG. 5d, a vector shift operation for an individual row 210 is shown, in which values 501, 502 in the first processing element 511 and processing elements 512 are shifted along the row 210 by being selectively loaded into neighbouring processing elements in series in the row 210. A value 503 in the last processing element 513 at the end of the row 210 is loaded into a further first processing element 514 in a lower row 510. A further value 505 in a further last processing element 515 in a lowest row 520 is loaded into the first processing element 511. This way, values can be shifted around the rows and columns of the array 200, without affecting the contents of the column edge registers. It will be appreciated by those skilled in the art that the shifting of values around the rows and columns of the processing element array, as shown in FIG. 5d, can occur in a direction opposite to that shown, i.e. the value in each processing element is loaded from a east neighbouring processing element and a value in a first processing elements in the row is shifted to the last processing element in a higher row.

[0159] The loading of a value into each processing element is selective, in that a processing element is only loaded from a connected processing element or column edge register when selected by its row and column select lines. The loading of values into each processing element only occurs from a neighbouring processing element, column edge register and/or connected processing element from the start or end of a row. Thus, a processing element, which is not selected to be loaded with a value itself, will still load a following processing element in its row and/or column with its value.

[0160] Referring to FIG. 6, an example of how data is broadcast from column edge registers 602 to processing elements in the array 200 is shown. A value 601 stored in one of the column edge registers 602 is output to the row bus 610 and is loaded into selected processing elements 604 which are selected by having both their row and column select lines 214, 216 activated with logical “1” values in row and column select registers 612, 614.

[0161] Referring to FIG. 7, an example of how a logical combination of values stored in selected processing elements 711, 712 is loaded into a column edge register 730 is shown (i.e. a broadcatch operation). When selected by its row and column select lines 214, 216, a first value 701 in a first selected processing element 711 is output to a neighbouring processing element 713 which is not selected and merely passes the first value 701 on to a second selected processing element 712 where it is combined with a second value 702 in a logical product to generate a result value 720. Since no further processing elements are selected in the row, the result value 720 is loaded into the column edge register 730. Such a logical combination is generated in each row and column for all of the processing elements having their row and column select lines 214, 216 activated with logical “1” values in the row and column select registers 612, 614.

[0162] Referring to FIG. 8a, an example of an array transformation operation using the shift operations described with reference to FIGS. 5a to 5 d above is shown. The transformation operation is a transposition of the data in array 200, for which use of a diagonal shift 802 of data between the processing elements is used.

[0163] The diagonal shift 802 is achieved by shifting data with pairs of row and column shift operations 802 a, 802 b as described above. The number of diagonal shifts, ‘N’, for each processing element required to achieve a complete transposition of the data in the processing element array 200 depends on the distance of each processing element 806 from a leading diagonal 804.

[0164] Referring to FIG. 8b, the array 200 is shown with a counter 806 for each processing element 821. A complete transposition operation of the, data stored in the array 200 is performed by decrementing the counter 820 on each diagonal shift 802. When a counter 820 in a given processing element reaches zero, the data in that processing element is not shifted any further and the neighbourhood connection register 308 in that processing element is loaded with its result value from the result register 306.

[0165] Each counter 820 starts with the value N, which is obtained for each processing element from the following expression:

[0166] (COL_INDEX+ROW_INDEX+1) mod ARRAY_SIZE

[0167] where COL_INDEX and ROW_INDEX are row and column indexes 822, 824 for a processing element. ARRAY_SIZE is a width/height 826 of the array. N.B. the aforementioned expression gives zero for all the processing elements on the leading diagonal as the values in these processing elements do not have to move.

[0168] Of course, the array transformation operation described in FIGS. 8a and 8 b above, is merely one example of a number of array transformation operations that can be carried out by application of the shift, broadcatch and broadcast operations described above.

[0169] In conclusion, through the introduction and use of the row and column select lines in the manner hereinbefore described, the present invention provides a more efficient and flexible parallel processor in which data is transferred between processing elements in the parallel processor.

[0170] It will of course be understood that the present invention has been described above purely by way of example and modifications of detail can be made within the scope of the invention. 

1. A parallel processor comprising: an array of processing elements arranged in rows and columns; for each column in the array, a column select line connecting to all of the processing elements in the column; and for each row in the array, a row select line connecting to all of the processing elements in the row, wherein a processing element in the array may be selected by activation of its row and column select lines.
 2. A parallel processor according to claim 1, further comprising, for each row in the array: a column edge register; and a row bus, the row bus connecting to all of the processing elements in the row and the relevant column edge register.
 3. A parallel processor according to claim 2, wherein in a first configuration: each processing element is adapted to load a value from the relevant row bus when selected by its row and column select lines; and the relevant column edge register is adapted to drive a value onto the row bus.
 4. A parallel processor according to claim 2, wherein: the row bus connects the relevant column edge register and all of the processing elements in the row in series; and in a second configuration: each processing element is further adapted to output onto the row bus a new value that is the logical combination of a value it loads from the row bus and a value internal to the processing element, when selected by its row and column select lines; and the relevant column edge register is further adapted to load from the row bus the said new value output by the last of the processing elements in the series.
 5. A parallel processor according to claim 4, wherein the said logical combination is a logical product.
 6. A parallel processor according to claim 1, further comprising, for each column in the array: a row edge register; and a column bus, the column bus connecting to all of the processing elements in the row and the relevant row edge register.
 7. A parallel processor according to claim 6, wherein in a third configuration: each processing element is adapted to load a value from the relevant column bus, when selected by its row and column select lines; and the relevant row edge register is adapted to drive the value onto the column bus.
 8. A parallel processor according to claim 6, wherein; the column bus connects the relevant row edge register and all of the processing elements in the column in series; and in a fourth configuration: each processing element is further adapted to output onto the column bus a new value that is the logical combination of the value it loads from the column bus and a value internal to the processing element, when selected by its row and column select lines; and the relevant row edge register is further adapted to load from the column bus the said new value output by the last of the processing elements in the series.
 9. A parallel processor according to claim 8, wherein the said logical combination is a logical product.
 10. A parallel processor according to claim 1, wherein each processing element is connected to one or more neighbouring processing elements and, in a fifth configuration, is adapted to load one or more values from one or more neighbouring processing elements when selected by its row and column select lines.
 12. A parallel processor according to any preceding claim, further comprising a control circuit in each processing element which receives and decodes control signals transmitted to all of the processing elements.
 12. A parallel processor according to any preceding claim, further comprising in each processing element: a neighbourhood connection register; and a selection circuit having a plurality of inputs and an output connected to an input of the neighbourhood connection register, wherein the selection circuit is adapted to select one of the plurality of inputs and output a value from the selected input to the neighbourhood connection register.
 13. A parallel processor according to claim 12, wherein a first input to the selection circuit is an output of the neighbourhood connection register in a neighbouring processing element on a first side in the column containing the processing element; a second input to the selection circuit is the column output of the interconnect circuit in a neighbouring processing element on a second side opposite to the first side; a third input to the selection circuit is an output of the neighbourhood connection register in a neighbouring processing element on a third side in the row containing the processing element; a fourth input to the selection circuit is the row output of the interconnect circuit in a neighbouring processing element on a fourth side opposite to the third side; and the control circuit is connected to the selection circuit and determines which one of the plurality of inputs outputs a value to the neighbourhood connection register.
 14. A parallel processor according to claim 13 comprising, for each row in the array: a column edge register; and a row bus, the row bus connecting to all of the processing elements in the row and the relevant column edge register; wherein in a processing element at the edge of the array not having a neighbouring processing element on the second side, the selection input corresponding to the neighbouring processing element is instead an output of the column edge register corresponding to the row of the processing element.
 15. A parallel processor according to claim 13 or claim 14 comprising, for each column in the array: a row edge register; and a column bus, the column bus connecting to all of the processing elements in the row and the relevant row edge register; wherein in a processing element at the edge of the array not having a neighbouring processing element on the fourth side, the fourth input to the selection circuit is an output of the row edge register corresponding to the column of the processing element.
 16. A parallel processor according to any one of claims 11-15, further comprising, in each processing element, an interconnect circuit having a plurality of inputs, a column output and a row output, wherein: a first input to the interconnect circuit is an output of the neighbourhood connection register; a second input to the interconnect circuit is the column output of the interconnect circuit in a neighbouring processing element in the column containing the processing element; a third input to the interconnect circuit is the row output of the interconnect circuit in a neighbouring processing element in the row containing the processing element; and the interconnect circuit is connected to the control circuit and is configured by the control circuit to direct to the column output either a value at the first input or a logical combination of a value at the first input and the second input and to direct to the row output either a value at the first input or a logical combination of a value at the first input and the third input.
 17. A parallel processor according to claim 16, wherein the logical combination is a logical product of the value at the first input and the second input or a logical product of he value at the first input and the third input.
 18. An active memory device comprising: a plurality of processing elements arranged in rows and columns; for each column: a row edge register; a column select line connecting to all of the processing elements in the column; a column bus connecting to all of the processing elements in the column and the relevant row edge register; for each row: a column edge register; a row select line connecting to all of the processing elements in the row; and a row bus connecting to all of the processing elements in the row and the relevant column edge register, wherein, for each processing element which is selected by activation of its row and column select lines, the relevant column edge register is adapted to drive a value onto the row bus and/or the relevant row edge register is adapted to drive a value onto the column bus, and each selected processing element is adapted to load the value from its row bus or the value from its column bus as the case may be.
 19. An active memory device comprising: a plurality of processing elements arranged in rows and columns; for each column: a row edge register; a column select line connecting to all of the processing elements in the column; a column bus connecting to all of the processing elements in the column and the relevant row edge register in series; for each row: a column edge register; a row select line connecting to all of the processing elements in the row; and a row bus connecting to all of the processing elements in the row and the relevant column edge register in series, wherein: each processing element, when selected by activation of its row and column select lines, is adapted to output onto the row bus a first value that is the logical combination of a value it loads from the row bus and a value internal to the processing element or is adapted to output onto the column bus a second value that is the logical combination of a value it loads from the column bus and the value internal to the processing element; and the relevant column edge register is further adapted to load from the row bus the said first value output by the last of the processing elements in the series in the row; or the relevant row edge register is further adapted to load from the column bus the said second value output by the last of the processing elements in the series in the column.
 20. An active memory device comprising: a plurality of processing elements arranged in rows and columns; for each column in the array, a column select line connecting to all of the processing elements in the column; and for each row in the array, a row select line connecting to all of the processing elements in the row, wherein each processing element is connected to one or more neighbouring processing elements and is adapted to load one or more values from one or more of the neighbouring processing elements when selected by activation of its row and column select lines.
 21. A method of operating a processing element in an array of processing elements arranged in rows and columns in a parallel processor, wherein there is provided for each column in the array, a column select line connecting to all of the processing elements in the column, and for each row in the array, a row select line connecting to all of the processing elements in the row, the method comprising: selecting a processing element in the array by activating its row and column select lines.
 22. A method according to claim 21, wherein there is provided, for each row in the array, a column edge register and a row bus, the row bus connecting to all of the processing elements in, the row and the relevant column edge register, the method further comprising: outputting a value stored in the column edge register corresponding to the selected processing element onto the row bus for the row; and loading the selected processing element with the value on the row bus.
 23. A method according to claim 21 or claim 22, in which there is provided, for each column in the array, a row edge register and a column bus, each column bus connecting to all of the processing elements in the column and the relevant row edge register, the method further comprising: outputting a value stored in the row edge register corresponding to the selected processing element onto the column bus for the column; and loading the selected processing element with the value on the column bus.
 24. A method according to any one of claims 21 to 23, in which there is provided a row bus connected to the relevant column edge register and all of the processing elements in the row in series, the method further comprising: outputting a value from each selected processing element to the row bus; logically combining the value with all other values output to the row bus from other selected processing elements in the row to generate a new value on the row bus; and loading the column edge register with the new value from the row bus.
 25. A method according to any one of claims 21 to 24, in which there is provided a column bus connected to the relevant row edge register and all of the processing elements in the column in series, the method further comprising: outputting a value from each selected processing element to the column bus; logically combining the value with all other values output to the column bus from other selected processing elements in the column to generate a new value on the column bus; and loading the row edge register with the new value from the column bus.
 26. A method according to any one of claims 21 to 24 further comprising: outputting a value from a neighbouring processing element to the selected processing element; and loading the value into the selected processing element. 